Methods for reduction of carbonyl compounds, such as ketones, carboxylic acid esters, lactones, carboxylic acid amides, and lactams, and imine compounds to obtain corresponding alcohols, amines, and the like are important in chemical synthesis. Considering the decrease in by-products, easy operation, labor safety, and the like, a catalytic reduction method, which uses a catalyst, in particular, is useful for producing alcohols, amines, and the like. As one of such reduction catalysts, for example, ruthenium complexes having a multidentate ligand are known.
Many methods have been proposed, such as a method for reduction of carboxylic acid esters by hydrogenation using, for example, a ruthenium complex having bidentate or quadridentate aminophosphine as a ligand (Patent Literature (PTL) 1 and 2), a ruthenium complex having tridentate aminodiphosphine as a ligand (PTL 3), or a ruthenium complex having pyridine ring as a ligand (PTL 4 and Non-patent Literature (NPL) 1).
Further, PTL 5 discloses a method for reduction of carboxylic acid esters by hydrogenation using a ruthenium complex that is obtained by reacting imidazolium salt having at least one optionally substituted amino group with a ruthenium compound in the presence of a base. PTL 5 discloses a ruthenium complex having an aminocarbene ligand, which is a bidentate ligand obtained by reacting an imidazolium salt with a base.